


Exorcist at Hogwarts

by Callie_Girl



Category: Constantine (TV), DCU, Harry Potter - J. K. Rowling
Genre: And sabotages Umbrige, British insults, He joins the DA, John Constantine at Hogwarts, no regrets, this is gonna be fun to write
Language: English
Status: In-Progress
Published: 2019-02-20
Updated: 2019-04-29
Packaged: 2019-11-01 10:24:29
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 5
Words: 3,970
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17865527
Author URL: https://archiveofourown.org/users/Callie_Girl/pseuds/Callie_Girl
Summary: John Constantine goes to Hogwarts and, while there, sabotages Umbridge in any way possible.





	1. 1

It was that damned demon.  
All he'd wanted was a normal exorcism, and this sonofabitch had decided to blast him god knows where. In the middle of some fucking woods! In the middle of the night.  
He moved through the trees. This place had a really magical feeling, and he was moving towards the epicentre. Hopefully, he was still in his world, or this was gonna be hard.  
An arrow shot into the tree right by his head. He moved back, searching for who's tried to kill him.  
Was that a centaur?!  
"Hey there, chap." he greeted. No reason to not be friendly, especially since there was another arrow pointed between his eyes. "I think there's been a bit of a mix-up-"  
"Silence!" The centaur roared. "Who are you?"  
"You can't have both!"  
The centaur was not amused. "Who. Are. You."  
"John Constantine. Exorcist, demonologist, occasional master of the dark arts, master warlock. Who might you be?"  
"I am Ronan!"  
"Ronan.. the centaur..." his eyes widened. Shit shit shit shit shit shit shit... "We got a big problem. So... here's what gonna happen; I'm gonna leave, go that way, you won't kill me and I won't kill you. Then I'll talk to Dumbbell and sort this out. Okay?"  
Ronan shook his head. "No. You will explain why you're in my woods."  
"I don't mean to be in your bloody woods!" Constantine shouted. He reached other his pocket, pulling out a box of cigarettes and lighting one.  
"How do you get into the woods without intending to?!" Ronan was getting agitated, and he could hear other centaurs on the way.  
"Great. Absolutely bloody marvellous," he growled. Well, a simple shield spell, and he just walked away.  
He was surprised when the centaurs let him leave.

It took two hours for him to get to the castles, and another to cross that huge fucking yard. That was after he crossed a lake. The spell for that hadn't worked as well as it normally did, so he was soaked to the bone and bitter. On the bright side, the sun was rising, and he could sense people in the castle waking up.  
Let's see... last time, he'd met Dumbledore in the Great Hall, so he'd try that. They'd left the bloody front door unlocked, so he strode in and tried to find it. That resulted in getting lost twelve and a half time times and encountering countless students. Which he was annoyed by. He had something to do, he couldn't stop to answer questions.  
What was fun was breaking up a duel by turning two magic wands into carnations.  
Eventually, he burst into the Great Hall. "Albus!"  
Before he even got halfway to the big table, a tiny woman in all pink with a really annoying voice stopped him and demanded to know who he was.  
"Well that ain't bloody important, now is it?" he growled annoyed.  
"How did you get in here?"  
"You left the bloody door open-"  
"You much leave at once!"  
"Alright, that's enough of you." he snapped, turning her into a snail. "Don't go anywhere."  
He glanced around the room as if to say 'anyone else' before going up to the staff table. "Dumbledore, we have a problem."


	2. 2

**Summary for the Chapter:**

> Let's piss of Umbridge, shall we? Sounds fun.  
> Also, Constantine arrived two weeks into the year

"Until we can find out how to send you back to your world, we have to do something with you," McGonagall said, lips pursed.  
Dumbledore smiled. "I have just the thing."  
John followed him through the stone passages and moving stairs, almost falling off some when they decided to move the second he tried to step on the landing. Dumbledore took him to what looked like a room dedicated to pink, full of bored students with the previously-snail witch back to human.  
"What's the meaning of this?" she demanded simperingly.  
"What's the meaning of your face?" John asked. A few students chuckled.  
"This is Mr Constantine. He's going to be your assistant."  
John's eyes widened a bit but he pretended to not be completely blindsided, because Umbridge was. "I beg your pardon?"  
"You heard him, you daft cow. I'm here to help."  
Umbridge ignored him. "He isn't Ministry approved!"  
"Yes. Well, he's Dumbledore approved." McGonagall said.  
John looked around the room, grabbing a book from a kid and studying it. This stuff was the kind they should be learning in the first year, not third. "Bloody hell." he looked over to where Umbridge was arguing with the other two. "Oi, cheese-eating surrender monkey!" yes, he was having fun. "What on Earth is this?"  
She huffed in annoyance. "That's what they're learning."  
He rubbed his eyes, sighing in frustration. This was the worst punishment ever.

He'd seen three periods of the most bored kids ever.  
He currently sat on his desk, watching the fifth years ask questions.  
Hermoine Granger's hand shot up. "There's nothing in here about using defensive spells."  
"Using them? I can't imagine why you would need to use defensive spells in my classroom."  
John stood up. "I can. Do I need to raise my bloody hand?"  
Not waiting for a response, he grabbed a spider. "Anyone have bay leaves? Also, I need... ah, there." he yanked one of Weasley's hairs, ignoring his yelp of shock. "Seriously, no one has bay leaves?"  
Hermione Granger raised her hand. "I can transfigure something."  
"Go on then, lass."  
She grabbed a paper, muttering something and tapping it with her wand. It turned into bay leaves, and he grabbed a handful, taking a bowl from his bag. Hair of ginger, bay leaves. He lit the mixture on fire.  
"Dilata est aranearum satanica potestas invoco posuerunt sub imperium. Tam facie mea. Nunc ea facere."   
The spider grew to the size of a rottweiler.  
"Now, someone take Weasley to the med bay. The spell has some adverse effects." as Longbottom, who was looking like he was about to pass out, took Weasley away, he turned to the class. "Now, if I were a bloody psychopath, I could use my spider here to kill all of you, and none would be able to defend themselves. Thankfully, I'm not..." the class sighed in relief. "I'm only a bit. On guard."  
Several people screamed. Only one in the front, Potter, looked confident.  
John laughed at all the scared people. "Oh relax, I'm not going to do that. Et undo mea carmina, et redire in statum pristinum haec aranea."  
The spider shrank and scurried off. Now he just had to deal with the pissed-off Umbridge. He smirked. "Eager to spend more time as a snail, are we love?"  
Finally, someone who was shorter than him.  
"Detention, Mr Constantine!" she shrilled.  
"I'm an adult! You can't give me detention."  
She smiled in a cruel way. "Then maybe act like one."

To get to his quarters, he had to go by Hufflepuff. Something had locked all of them out, so the entire house was just crowded by the door. He raised an eyebrow. "What does it take to open?"  
"A password. But it won't open."  
"Well... if you don't mind fixing the door, I can help."  
"We just need to get inside. We've got classes after break."  
He nodded. He wouldn't be able to undo the magic on the door, but there was always the low-tech way.  
He kicked it in. Students thanked him as they went inside, and he started back to his original task. At the last minute, he changed his mind, going to the opposite end of the school, to where the potions master was. He needed some ingredients for a spell.

"Alright, potion guy. Do you have anything on this list?" Snape glared at the list.  
"What do you need horn of bicorn for?"  
"Ah... do you have it in powder form, mate? I need it for a spell."  
"And... aluminium flower?"  
"Dried, if you can."  
Snape looked at him. "I have all of these, but I want to know what you intend to do."  
"First is a spell to see someone's true intentions. Then I need to ward myself against the poltergeist. Then, I need to summon my wand from another dimension and my spell book."  
Snape nodded. "I'll be back."  
Constantine smiled. Of course, he couldn't say what most of the ingredients. But, Umbridge was going DOWN.


	3. 3

**Summary for the Chapter:**

> Here is where some major canon divergence starts. I apologize.  
> Also, yes, Hermione is black.

You could see their plans from a kilometre away.  
Honestly, a bloke with half a mind would know that there was something wrong with all these students going to Hogs Head on the same day. A simple glamour and he was a striking you Hufflepuff lad who sat in the back of the meeting. No one paid any attention to him, except the odd look every once in a while.  
He listened to Harry Potters plan about teaching others how to defend themselves, and he liked it. The boy was a damned fool for not already having a set location, but if he could teach this clueless lot how to muster a decent shield charm, more power to him.  
He signed the paper, leaving a note for them before leaving.

If you need help finding a base, see me after class  
-John Constantine.

 

As he predicted, the golden trio of this generation came up to him after class. He led them to his quarters, noting how nervous they were.  
“You were at the meeting.” It wasn’t a question. Weasle was making an accusation.  
“I was at the meeting.” John agreed.  
“Who were you?”  
“Dashing young Hufflepuff in the back. The one none of you realized that you didn’t know.”  
“I knew there was something wrong with that kid,” Hermione whispered.  
“You could’ve done something about it, lass. What if a young Slytherin woman had been Umbridge?”  
Hermione baulked. “Slytherin isn’t THAT evil.”  
The four cracked up.  
“Well, look. If you need a base, I know three locations in this school that no one else does. Locations with strong magick that takes hell to get into if you don’t know what it takes.”  
“How do we know we can trust you?” Harry asked. Smart boy.  
“Well, I signed your cursed paper, didn’t I?” he’d taken the spell off of himself, of course, but he wasn’t telling them that. “How about this? I’ll take you three to one of the locations, but it would be easier if I had all of you. Potion ingredients don’t come by cheap, you know.”  
Harry nodded. “Where do you need us to meet you?”  
“By the lake, where it meets the Forbidden Forest. I’ll cast a glamour on the place so that Umbridge can’t see it. Before lunch tomorrow.” he smirked. “The place we’re going will provide us with what we need.”

Sure enough, they all met him where he asked.  
He examined the group. “Don’t try to copy what I’m about to do. The magick is far beyond your level.”  
Hermione seemed to take that as a challenge.  
“Ravenclaw pates vocat, de cultissima Hogwarts quatour. Ego auctoritate puniri martimos aestus Maximos intempore hoc loco apositi sunt ei serve meus, et invocabo libidini obnoxious. Ego praecipio tibi!” he poured the potion on the grass, smiling as the water began to part, clearing a dry path to a ship at the very bottom of the lake. This time, it was a cargo ship.  
“Well, chop chop. Before the spell wears off.” the students were nervous but followed him when he walked towards the ship. The magick, recognizing him, opened the colossal doors at his command.  
“Now that you lot have been here, the magick will recognize you. You won’t need me or a potion to get back here next time,” he explained, snapping to turn on the lights. They were in a training room.  
“What is this place?” Longbottom demanded.   
John nodded. “You’ve heard of the Chamber of Secrets?”  
“Yeah.”  
“Each of the Hogwarts four had their own stronghold. Slytherin is easiest to access, Hufflepuff is the hardest. This is the stronghold of Ravenclaw. You want to know why Hogwarts is where it is?”  
Everyone nodded.  
“This place is one of seven where wild, true magick escapes into the world. Magick with a k, not the wand-waving bollocks you lot do. The Hogwarts four recognized this place for its value and created a school here so that others may feel the power. This place is as old as God hisself and almost as powerful. Anybody hungry?”  
Again, everyone nodded.  
“Okay. Picture the food you want most and follow me.” it was getting depressing, how easily they followed his orders. He led them to the kitchen, unsurprised to find it covered in all manner of foods. The students gasped, each running to their own plate and eating like they’d been starved for a minute and a half.  
He left, walking to the library with his second potion. He walked to the apothecary portion, finding a stockpile of rare and expensive ingredients that he didn’t even dare ask Snape for. He grabbed horns of a Battletoad, a tentacle of Cthulhu, hair of a Capricorn, and powdered dinoshark teeth. He added them to an obsidian bowl, mixing it thoroughly and chanting something in Enochian.  
There was a dramatic-arse flash, and something wood appeared in his right hand. His wand, black Thornwood with Capricorn hair and grass from the tomb of Jesus. It was a Gregorovitch model, one of a kind. Powerful. And it would survive him holding it while he fell down the stairs, which is always a bonus.  
“What kind of magic is that?” he spun, seeing the dark face and curly hair of Hermione Granger.  
“It’s… Enochian. Very dangerous magick. Gives you access to things that are wild and unpredictable because that’s what magick is. I’ve studied it for most of my life and even now it’s really bloody dangerous.” he pointed at her warningly. “Don’t try it. You could easily wind up damning yourself to hell. Or worse. Expelled.”  
“Is it anything like wicca?” she asked, examining a scry.  
He blinked. “A bit. Enochian magick uses potions and mixtures and all that bollocks. But it’s not tied to any religion unless you want to get into the whole language-of-the-angels thing.”  
“Why are we never taught that it exists?”  
“Number one, dangerous. Number two, it originates from my dimension. Here, magic is waving a wand and speaking a funny language. Now, any more questions?”  
She shook her head.  
“Well, this first day was just to get the magick used to you. You lot can decide on when the next meeting is, or if you even want to have it here. I’d hurry, lass.” he smirked. “Lunch is over in fifteen minutes.”  
He didn’t see her stuff two books into her bag.


	4. 4

**Summary for the Chapter:**

> John gets to be a substitute

The cooking wasn't as good as what Chas could make, but breakfast was still good. He couldn't help but notice that Umbridge never showed up, and he found himself hoping she was dead.

Near the end of the meal, Dumbledore came over. "Good morning, John."

"G'morning."

"Professor Umbridge has been called away on urgent Ministry business, and is thus unable to teach her class. We were wondering if you could fill the role for today?"

John sighed, putting down his lighter. "Fine. But just today."

This was going to be a disaster.

 

The class buzzed with curiosity as Constantine walked in, sitting on Umbridge's desk and shoving some of the junk on top of it to the floor. "A'ight... not quite sure what I' supposed to teach you lot, so does anyone have any questions?"

Hermione Granger's hand shot up. "What kind of work do you do?"

"I am an exorcist, demonologist, and... petty dabbler in the dark arts. Sometimes I time travel, save the universe... average Tuesday morning."

Harry raised his hand, "do you know who Voldemort is?"

Constantine snorted. "Know who he is? I met the wanker. Last time I was here, Voldy was at school, opening Chambers of Secrets and framing innocent half-giants."

Someone else spoke up, "But... you can't be THAT old... that was almost fifty years ago!"

"Well, for me it was two years ago. That's the funny thing about both time travel and exploring alternate realities... time doesn't work proper."

"Alternate realities, sir?"

"Parallel planes of existence. I come from a world where Hogwarts is a fictional place, part of a book series written by a clairvoyant named JK Rowling. I would honestly love to tell you lot exactly how all this turns out... but screwing up the timeline would kill all of us, and cause a severe anachronism in the timelines of multiple other realities."  
More hands shot up, and he found himself teaching all the little bastards about his own reality. He also explained bits and pieces of the Enochian magick they'd seen him use.

Then, there was a concealed threat.

Draco Malfoy interrupted. "What do you know about the Hogwarts Four? If Slytherin had his own base, the others must've too, right?"

He didn't stiffen, he was too professional for that. he took another drag from his cigarette. "Can't admit to knowing much about that lot, honestly. As for the 'base' bollocks... well, they very well could. But you gotta remember that these four were extremely powerful warlocks of old. Even if they did have bases, you would need to be extremely talented and experienced to find them. More than any of your levels, I tell you."

"What do you mean, our levels?"

"Hmmm... well, let me put it this way. I'm a level 25 warlock, which is very bloody impressive. If I were to hit any of you lot with a killing curse, odds are I could even get it to ricochet and take out at least five other people. If any of you lot tried the same on me, the most you would do is give me a migraine. Sure, I can give a few who could knock me out cold, but most of you wouldn't even make me blink."

"Are you sure you don't know anything?" Malfoy drawled.

John rose. "If you're accusing me of something, bloody say it."

This evolved into a two-minute staring contest between Malfoy and Constantine, until someone asked, "Can you show us some of that Enochian stuff you were talking about?"

"Well... Enochian is far too dangerous to use in such close quarters. But I can show you a different type." he grabbed a pen from his pocket. "My friend Z specializes in this type. Not quite sure what it's called, but this is a simple changing spell." he focused on the pen, envisioning the words in his head, then how they would be if they were backwards. "Egnahc eht ruoloc ot neerg!"

The pen became bright green, and a few people gasped. The bell rang, and he called, "Harry, Ron, Hermione, can I talk to you lot for a sec?"

After the others were gone, he cast a silencing spell on the door. "A'ight, call the DA meeting off."

"What? Why?"

"You heard what Malfoy was saying. He knows something..."

"How can you tell?

"After all the insane hints he was dropping? Hard not to. You honestly think it's a coincidence Malfoy makes those comments on the same day Umbridge is gone, and on the same day we have a meeting? Nah, I don't bloody buy it."

Harry nodded slowly. "Okay. We'll get the message out."


	5. Headaches

**Summary for the Chapter:**

> There's something creeping around the school, and John is the only one who knows.

John watched Umbridge, trying to gauge if she knew anything. It was droll, trying to pay attention to her, and he found himself nodding off, leaning against the wall...

/He was standing in a long, dark corridor, his feet moving of his own accord, taking him closer and closer to a shimmering black door. As he got closer, voices began to play, vying for his attention... Des, Astra, Gaz... Thousands more, screaming, tormented voices, begging for him to help them. Accusing him that their agony was his fault... Despite this, he continued to move forward, and the screams kept getting louder.  
Finally, he reached the door. His hand reached out to it, and to his horror, he saw that it wasn't his hand. This hand was porcelain white, with claws, and an armed clothed in a sweeping black cloak. It reached out to touch the door, and.../

"John! JOHN!" Hermoine Granger was leaning over him. He groaned.

"What jus' happened?"

"You had a seizure. Fell to the ground and started to convulse."

"Don't forget to tell him he's in a pool of blood," Patil warned.

"There's also that." John sat up, taking the offered tissue and wiping the blood from his face. Hermione pointed her wand at him, using a cleaning spell to erase the blood from his clothes, then the floor.

"You need to go to Madame Pomfrey. A seizure is very serious." Hermoine informed. He forced himself to his feet.

"That's a smashing idea, luv. I'll... I'll get righ' on it..." he stumbled out of the classroom, half leaving on the wall as he tried to make his way to the hospital wing until his legs collapsed and he decided to just stay on the floor.

Nearly Headless Nick eventually floated by and did a double take. "Are you alright?"

"Not really. Gotta get to the hospital wing, but I can't."

Nick nodded. "I'll alert Madame Pomfrey."

"Thanks."

 

Eventually, Pomfrey came. "What on Earth happened to you?!"

"Seizure, I think."

She sighed, conjuring a stretcher. He mustered the energy to lay on it, and she levitated it to the hospital wing. After what felt like hours of poking and prodding, she came to a conclusion. "It wasn't a seizure. Something magical is ailing you. I can heal the lasting effects, but if it happens again I may have to send you to St Mungo's. I'm also going to make you stay here for the rest of today, and through the night, too." she paused as if she expected him to argue, then whisked away. He removed his coat, shoes, and tie, then conjured a heavy blanket and quickly fell back asleep.

 

When he woke up again, he found his bedside table covered in all manner of candies. "Bloody hell! Where'd all this come from?"

"Students. Dumbledore also sent a few chocolate frogs. How are you feeling?"

The walls went up again. He was never one to admit that he felt shoddy, and he wasn't going to start now. "I feel perfectly fine, luv. Just need a bit more bedrest."

She huffed in a way that implied she didn't believe a word he was saying, then walked off.

He was halfway through sorting the pile of candies when he found baked cinnamon apples with a card signed, "I find this gets the headaches away. -Harry Potter."

A brief inspection turned up nothing wrong with the apples, so John ate them. They were pretty good, and Potter was right; they did get rid of the headache. Almost instantly. He was wondering how Potter knew about the cure when Pomfrey escorted the kid over.

"Did you get the apples?" Harry asked.

"Aye. How did you know-"

"I recognized all the symptoms of Voldemort dreams. The first time's always the worst, and you should feel better by tomorrow... What was he doing? Was it the door?"

"Yeah... but where?"

"I don't know." Harry seemed deeply disturbed. "But whatever's behind it, he wants it really bad."

 

John decided to skip breakfast, stay in his room until he knew Umbridge would be occupied. Then he would cast a spell to shield himself from Voldemort because he couldn't afford to pass out every time the wanker went into his head.

He was just passing Hufflepuff when he heard an indistinct whisper. Suddenly, he started walking in a different direction. Up the stairs. Into Moaning Myrtle's bathroom. She stared at him as he went to the sink, and a strange hissing sound issued from his mouth.

The sink opened up, revealing a tunnel.

And he stepped into it.


End file.
